Process for producing perylene-3, 4-dicarboxylic acid imides

ABSTRACT

Perylene-3,4-dicarboximides I ##STR1## (R 1  is hydrogen; C 1  -C 8  -alkyl; C 5  -C 8  -cycloalkyl; substituted or unsubstituted phenyl or naphthyl; 
     R 2  independently at each occurrence is hydrogen; C 1  -C 18  -alkyl, substituted or unsubstituted aryloxy, arylthio, hetaryloxy or hetarylthio) 
     are prepared by reacting the corresponding perylene-3,4,9,10-tetracarboxylic acid or its anhydride (II) with an amide III 
     
         R.sup.3 --CO--NHR.sup.1                                    III 
    
     (R 3  : C 1  -C 4  -alkyl or --NR 4  R 5  where R 4  and R 5  independently are hydrogen or one of the R 1  alkyls, cycloalkyls, phenyls or naphthyls and where if two or more of R 1 , R 4  and R 5  are other than hydrogen they are identical) 
     under superatmospheric pressure in the presence of an inert diluent and a transition metal catalyst.

The present invention relates to a novel process for preparingperylene-3,4-dicarboximides of the formula I ##STR2## where R¹ ishydrogen; C₁ -C₈ -alkyl; C₅ -C₈ -cycloalkyl; or phenyl or naphthyl, eachof which can be substituted by C₁ -C₁₀ -alkyl, C₁ -C₆ -alkoxy or cyano;and

R² independently at each occurrence is hydrogen; C₁ -C₁₈ -alkyl; oraryloxy, arylthio, hetaryloxy or hetarylthio, each of which can besubstituted by C₁ -C₁₀ -alkyl, C₁ -C₆ -alkoxy or cyano.

Perylene-3,4-dicarboximides of the formula I are known to be importantintermediates in preparing pigment additives, fluorescent dyes andfluorescent pigments (EP-A-636 666; EP-A-596 292), but are also suitablethemselves with advantage as fluorescent dyes and pigments (EP-A-657436; nonprior-published DE-A-195 01 737).

To prepare perylene-3,4-dicarboximides I whose perylene framework isunsubstituted (R² ═H) a range of complex multistage processes have beendescribed which start from perylene-3,4,9,10-tetracarboxylic dianhydrideand which yield the compounds I in usually unsatisfactory yields and insuch poor purity that complex purification methods, such as extractionand column chromatography, are required.

For instance, unsubstituted and N-alkyl-substitutedperylene-3,4-dicarboximides (where alkyl is methyl, ethyl, n-propyl,n-butyl, isobutyl, n-pentyl, n-hexyl, n-octyl or n-dodecyl) are obtainedby alkaline decarboxylation of the perylene-3,4,9,10-tetracarboxylicimide anhydride intermediates at ≧220° C. under superatmosphericpressure in reaction times of 18 h (DE-C-486 491; Bull. Chem. Soc. Jap.54 (1981) 1575-1576; EP-A-596 292). This process, however, is suitableonly for base-stable aliphatic imides.

To prepare the N-methyl- and N-ethyl- (and also N-phenyl-, N-tolyl- andN-anisyl-)substituted perylene-3,4-dicarboximides, the initiallyprepared unsubstituted perylene-3,4-dicarboximide is sulfonated witholeum and then converted with potassium hydroxide solution into thesulfonated anhydride, which is then reacted with the appropriate primaryamine to form the sulfonated N-substituted imide, which finally isdesulfonated using sulfuric acid to give the desiredperylene-3,4-dicarboximide (Bull. Chem. Soc. Jap. 52 (1979) 1723-1726,Shikizai Kyokaishi 49 (1976) 29-34 = Chemical Abstracts 85:209285). Thisprocess is extremely laborious and can only be used forsulfuric-acid-stable imides.

In EP-A-657 436, unsubstituted, N-alkyl-, N-cycloalkyl- andN-phenyl-substituted perylene-3,4-dicarboximides with an unsubstitutedperylene framework are obtained by condensingperylene-3,4,9,10-tetracarboxylic dianhydride with2,5-di-tert-butylaniline in the presence of water, zinc acetatedihydrate and imidazol, by alkaline hydrolysis of thechromatographically purifiedN-2,5-di-tert-butylphenylperylenedicarboximide, to give theperylene-3,4-dicarboxylic anhydride, which is then reacted with theappropriate primary amine.

Another process described in EP-A-657 436 for preparingN-alkyl-substituted perylene-3,4-dicarboximides starts from theunsubstituted perylene-3,4-dicarboximide, which initially, as describedabove, can be prepared from perylene-3,4,9,10-tetracarboxylicdianhydride and is reacted with the appropriate alkyl bromide in thepresence of a strong base and of a dipolar-aprotic solvent. In this casetoo the reaction products are chromatographed.

Finally, N-1-hexylheptyl- and N-1-octylnonyl-perylene-3,4-dicarboximidecan in accordance with EP-A-657 436 also be obtained, by analogy withthe N-2,5-di-tert-butylphenylperylene-3,4-dicarboximide intermediate,directly from perylene-3,4,9,10-tetracarboxylic dianhydride.

However, the preparation processes known from EP-A-657 436 as well arehighly complex and produce only low overall yields of the N-substitutedperylene-3,4-dicarboximides.

A process which is suitable inter alia for preparingperylene-3,4-dicarboximides which are substituted in the peryleneframework is described in nonprior-published DE-A-195 01 737. Here, theimides I are obtained by direct reaction ofperylene-3,4,9,10-tetracarboxylic dianhydride and primary amine in thepresence of a tertiary nitrogen-basic compound, such as quinoline, andof zinc, copper or salts thereof as catalyst, without the addition ofwater.

It is the object of the present invention to provide a simple andeconomic process which is unhampered by the above disadvantages andwhich permits the preparation of perylene-3,4-dicarboximides, which maybe substituted on the imide nitrogen and/or in the perylene framework,in good yields and in purities sufficient for the subsequent intendeduse.

We have found that this object is achieved by a process for preparingperylene-3,4-dicarboximides of the formula I ##STR3## where R¹ ishydrogen; C₁ -C₈ -alkyl; C₅ -C₈ -cycloalkyl; or phenyl or naphthyl, eachof which can be substituted by C₁ -C₁₀ -alkyl, C₁ -C₆ -alkoxy or cyano;and

R² independently at each occurrence is hydrogen; C₁ -C₁₈ -alkyl; oraryloxy, arylthio, hetaryloxy or hetarylthio, each of which can besubstituted by C₁ -C₁₀ -alkyl, C₁ -C₆ -alkoxy or cyano,

which comprises reacting a perylene-3,4,9,10-tetracarboxylic acid or itsanhydride of the formula II ##STR4## with an amide of the formula III

    R.sup.3 --CO--NHR.sup.1                                    III

in which R³ is hydrogen, C₁ -C₄ -alkyl or --NR⁴ R⁵ where R⁴ and R⁵independently are hydrogen or one of the R¹ alkyls, cycloalkyls, phenylsor naphthyls and where if two or more of R¹, R⁴ and R⁵ are other thanhydrogen they are identical in the presence of an inert diluent and atransition metal catalyst and under superatmospheric pressure.

The alkyls in formulae I, II and III may be either straight-chain orbranched. Substituted aryl may generally carry up to 3, preferably 1 or2, of the substituents mentioned.

Specific examples of suitable radicals R¹ -R⁵ (or substituents thereof)are:

methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl,isopentyl, neopentyl, tert-pentyl, hexyl, 2-methylpentyl, heptyl,1-ethylpentyl, octyl, 2-ethylhexyl, isooctyl, nonyl, isononyl, decyl,isodecyl, undecyl, dodecyl, tridecyl, isotridecyl, tetradecyl,pentadecyl, hexadecyl, heptadecyl and octadecyl (isooctyl, isononyl,isodecyl and isotridecyl are trivial names originating from the alcoholsobtained by oxo synthesis--cf. Ullmanns Encyklopadie der technischenChemie, 4th Edition, Volume 7, pages 215-217 and Volume 11, pages 435and 436);

methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, tert-butoxy,pentoxy, isopentoxy, neopentoxy, tert-pentoxy and hexoxy;

phenyl, 2-naphthyl, 2-, 3- and 4-methylphenyl, 2,4-, 3,5- and2,6-dimethylphenyl, 2,4,6-trimethylphenyl, 2-, 3- and 4-ethylphenyl,2,4-, 3,5- and 2,6-diethylphenyl, 2,4,6-triethylphenyl, 2-, 3- and4-propylphenyl, 2,4-, 3,5- and 2,6-dipropylphenyl,2,4,6-tripropylphenyl, 2-, 3- and 4-isopropylphenyl, 2,4-, 3,5- and2,6-diisopropylphenyl, 2,4,6-triisopropylphenyl, 2-, 3- and4-butylphenyl, 2,4-, 3,5- and 2,6-dibutylphenyl, 2,4,6-tributylphenyl,2-, 3- and 4-isobutylphenyl, 2,4-, 3,5 and 2,6-diisobutylphenyl,2,4,6-triisobutylphenyl, 2-, 3- and 4-sec-butylphenyl, 2,4-, 3,5- and2,6-di-sec-butylphenyl and 2,4,6-tri-sec-butylphenyl; 2-, 3- and4-methoxyphenyl, 2,4-, 3,5- and 2,6-dimethoxyphenyl,2,4,6-trimethoxyphenyl, 2-, 3- and 4-ethoxyphenyl, 2,4-, 3,5- and2,6-diethoxyphenyl, 2,4,6-triethoxyphenyl, 2-, 3- and 4-propoxyphenyl,2,4-, 3,5- and 2,6-dipropoxyphenyl, 2-, 3- and 4-isopropoxyphenyl, 2,4-and 2,6-diisopropoxyphenyl and 2-, 3- and 4-butoxyphenyl; 2-, 3- and4-cyanophenyl;

phenoxy, phenylthio, 2-naphthoxy, 2-naphthylthio, 2-, 3- and4-pyridyloxy, 2-, 3- and 4-pyridylthio, 2-, 4- and 5-pyrimidyloxy and2-, 4- and 5-pyrimidylthio.

In the novel process for preparing the perylene-3,4-dicarboximides I,the perylene-3,4,9,10-tetracarboxylic dianhydrides II (or thecorresponding acids) are not as with customary imidations reacted withprimary amines but with amides of the formula III as amine equivalents,which facilitate controlled direction of the reaction, including inparticular extensive suppression of the disruptive side reaction formingthe unwanted perylenetetracarboxylic diimides and also permit thepreparation of the N-C₁ -C₄ -alkyl imides I and the unsubstituted imidesI.

Suitable amides III are both the appropriate N-substituted orunsubstituted amides (R¹ =H) of aliphatic C₁ -C₄ carboxylic acids,especially formic acid and acetic acid (case a) and also urea (R¹ =H)and the appropriate N-monosubstituted, N,N- and N,N'-disubstituted andN,N,N'-trisubstituted urea derivatives (R¹ ≠H; case b). Preferred amidesIII are those which are at least partly soluble in the diluent used,since such amides can advantageously be added to the reaction mixture asa solution during the reaction in a controlled (continuous or elsediscontinuous) manner.

The carboxamides IlIa are preferably used to prepareperylene-3,4-dicarboximides of the formula I in which R¹ is (especiallyunbranched) C₁ -C₄ -alkyl or in particular is hydrogen or aryl.

The urea derivatives IIIb, especially the disubstituted and inparticular the monosubstituted derivatives, can be used with advantagefor preparing all perylene-3,4-dicarboximides I, including those whereR¹ comprises branched and/or higher alkyl, cycloalkyl and aryl.

Specific examples of particularly suitable amides III are formamide,acetamide, N-methyl-, N-ethyl-, N-n-propyl- and N-n-butyl-, N-phenyl-,N-o-tolyl- and N-p-tolylformamide and -acetamide, urea, N-methyl-,N-ethyl-, N-propyl-, N-butyl-, N-pentyl-, N-hexyl-, N-heptyl- andN-octylurea, N,N- and N,N'-dimethyl- and N,N- and N,N'-diethylurea, andN-cyclopentyl-, N-cyclohexyl-, N-cycloheptyl-, N-cyclooctyl-, N-phenyl-,N-o-tolyl-, N-p-tolyl- and N-2-naphthylurea.

When the carboxamides IIIa are used the molar ratio ofperylene-3,4,9,10-tetracarboxylic dianhydride II to IIIa is generallyfrom 0.5:1 to 1.2:1, preferably from 0.9:1 to 1.1:1.

When urea and its derivatives IIIb are used, the molar ratio of II toIIIb is generally from 0.9:1 to 2.5:1, in the case of mono- andtrisubstituted ureas preferably from 0.9:1 to 1.1:1, and in the case ofurea itself and of disubstituted ureas preferably from 1.8:1 to 2.2:1.

The novel reaction of the perylene-3,4,9,10-tetracarboxylic dianhydridesII (or the corresponding acids) with the amides III is carried out inthe presence of an inert diluent and a transition metal catalyst andunder superatmospheric pressure.

Suitable diluents for this reaction are preferably tertiary nitrogenbases, for example cyclic imides, such as N-methylpyrrolidone, tertiaryaliphatic amines NR₃ whose alkyl radicals R have 4 to 8 carbons, such astrihexylamine, and, in particular, aromatic heterocycles, such aspyridine, quinaldine, isoquinoline and especially quinoline.

The amount of diluent is not critical per se and is usually from 2 to 12kg, preferably from 4 to 8 kg, per kg ofperylene-3,4,9,10-tetracarboxylic dianhydride II.

Suitable transition metal catalysts other than zinc and its salts are,in particular, copper and its inorganic and organic salts, which arepreferably employed in anhydrous form.

Examples of preferred salts are copper (I) oxide, copper (II) oxide,copper (I) chloride, copper (II) chloride, copper (I) bromide, copper(II) bromide, copper (II) acetate, copper (II) acetylacetonate, basiccopper (II) carbonate and copper (II) sulfate.

Mixtures of the catalysts mentioned can also be used, of course.

In general the amount of catalyst used is from 20 to 150% by weight,preferably from 25 to 60% by weight, based on theperylene-3,4,9,10-tetracarboxylic dianhydride II.

The novel preparation process is expediently carried out in a closed,stirred pressure vessel (autoclave) under autogenous pressure, ie. thepressure established automatically in the closed system. In this case,during the reaction and depending on the chosen reaction conditions (forexample the temperature of in general 120 to 250° C., preferably 160 to200° C.), it is possible for a pressure of up to 25 bar to becomeestablished. Preference, however, is given to pressures of up to 18 bar.

It is advisable to operate under an inert gas atmosphere (for examplenitrogen).

The novel reaction is normally over in 2 to 30 h, especially 3 to 12 h.

In terms of procedure the novel process can be carried out by adding allof the amide III at once to the reaction mixture before the latter isheated to reaction temperature, or metering in the amide III (preferablycontinuously), dissolved in a portion of the diluent used, into thereaction mixture which has been heated to reaction temperature.

In the former case, an expedient procedure is as follows:

The apparatus is charged with perylene-3,4,9,10-tetracarboxylicdianhydride II, catalyst and amide III in the entire quantity of diluentand the pressure apparatus is flushed with nitrogen (for about 15minutes). After the apparatus has been closed, the mixture is heatedwith stirring to reaction temperature where it is stirred for about 3 to8 h.

After the mixture has been cooled to a temperature of normally 20 to 50°C. and the apparatus has been let down, the reaction mixture can beworked up in accordance with one of the following variants:

Generally, about 1 to 1.5 times the amount of alcohol, preferablymethanol, is added to the reaction mixture and the precipitated crudeproduct is filtered off. Unreacted perylene-3,4,9,10-tetracarboxylicdianhydride II can be removed subsequently by stirring the product forfrom 0.5 to 1 hour in from about 6 to 10 times the amount of hot, diluteinorganic base (eg. 10% strength by weight potassium carbonate solutionor 5 to 10% strength by weight potassium hydroxide solution), filteringthe mixture again and washing the product first of all with a hotaqueous base, until the run off is colorless, and then with water untilthe run off is neutral.

Generally, from about 1 to 1.5 times the amount of alkyl acetate,especially C₁ -C₄ -alkyl acetate and, in particular, ethyl acetate isadded to the reaction mixture, and the precipitated product is filteredoff and washed first with further alkyl acetate until the run off iscolorless and then with water to free it from solvent.

In both variants, complete removal of the catalyst can be effected bysubsequently boiling the filter cake in dilute inorganic acid (forexample 10-15% strength by weight hydrochloric acid) for 0.5 to 1 h.

Subsequently, the imides I can be isolated as usual by filtering thecooled mixture, washing the product with water until the aqueous run offis neutral and salt-free, and drying the product. In the second of thepossible preparation procedures mentioned earlier,perylene-3,4,9,10-tetracarboxylic dianhydride II and catalyst areinitially introduced in only a portion of the diluent (for example abouthalf) and then, as described above, the mixture is flushed withnitrogen, the apparatus is closed and the mixture is heated to reactiontemperature, before metering in the amide III, dissolved in the rest ofthe diluent, at a constant volume flow rate over the course of about 4to 8 h. Following an after-stirring time of about 0.5 to 8 h, thereaction mixture is cooled, normally to 20-50° C., and the apparatus islet down. Subsequent working up can be carried out in a manner describedabove.

In general the products I treated in this way are already of such highpurity (>80%) that further purification is unnecessary.

However, if it is desired to increase the purity to >98%, then theperylene-3,4-dicarboximides I can be subjected further to thepurification techniques described in the nonprior-published DE-A-195 01737, by first heating them in N-methylpyrrolidone and then treating theresulting N-methylpyrrolidone adducts with a base (especially an aqueousalkali metal hydroxide) under hot conditions and in the presence of anorganic diluent (especially an aliphatic alcohol such as isopropanol),and subjecting if desired the subsequently isolated products to anadditional treatment with a dilute inorganic acid (especiallyhydrochloric acid).

The novel preparation process can be used to prepare bothperylene-3,4-dicarboximides which are substituted in the peryleneframework and those which are unsubstituted in high yields(generally >70%) and high purities in an advantageous, simple andeconomic manner. In particular, it is also possible readily to obtainthe perylene-3,4-dicarboximides I which are substituted by lower alkyl(C₁ -C₄ -alkyl, especially methyl) or are unsubstituted on the imidenitrogen.

EXAMPLES

Preparation of perylene-3,4-dicarboximides of the formula Ia ##STR5##from perylene-3,4,9,10-tetracarboxylic dianhydrides of the formula IIa##STR6##

Examples 1 to 17

Process variant 1 (V1)

In a 1 l stirred pressure vessel, a mixture of 0.15 mol of theperylene-3,4,9,10-tetracarboxylic dianhydride IIa, 0.15 mol of the amideIII (Example 1: 0.075 mol of urea; Examples 5 to 7: 0.075 mol ofdimethylurea) and x g of the catalyst K in 300 ml of quinoline wasflushed with nitrogen for 15 minutes. After the vessel had been given apressure-tight seal, its contents were heated to T° C. with stirring andwere maintained at this temperature for t h.

After cooling to room temperature and letting down of the reactionvessel, 400 ml of methanol were added to the reaction mixture. The crudeproduct precipitated in this way was filtered off over a G3 glass fritand was washed with methanol until free from quinoline.

For further purification, the crude product was slurried in 500 ml ofhot 10% strength by weight aqueous potassium carbonate solution, stirredat 80° C. for 1 h, filtered off again and washed first with hotpotassium carbonate solution, until the run off was colorless, and thenwith water to neutrality. For complete removal of the catalyst, thefilter cake was subsequently boiled in 500 ml of 10% strength by weighthydrochloric acid for 1 h, filtered off, washed with water until neutraland free from salt, and dried.

Process variant 2 (V2)

In a 1 l stirred pressure vessel, a mixture of 0.15 mol of theperylene-3,4,9,10-tetracarboxylic dianhydride IIa and x g of thecatalyst K in 250 ml of quinoline was flushed with nitrogen for 15minutes. After the vessel had been given a pressure-tight seal, itscontents were heated with stirring to T° C. At this temperature, asolution of 0.15 mol of the amide III in 50 ml of quinoline (Example 8:+20 ml of N-methylpyrrolidone to increase the solubility) were meteredin continuously via a pump over t₁ h.

Following an after-stirring time of t₂ h at T° C., the reaction mixturewas cooled to room temperature, the apparatus was let down and thereaction mixture was worked up as described for process variant V1.

Further details of these experiments and their results, including thepurities determined by quantitative thin-layer chromatography on silicagel against high-purity standards using a trichloroacetic acid/toluenemixture (1:3 to 1:10 v/v) as eluent, are compiled in the table below.

Note regarding Example 11:

The 1,7-diphenoxyperylene-3,4,9,10-tetracarboxylic dianhydride employedwas obtained as described in the earlier German Patent Application 19547 209.8 by brominating perylene-3,4,9,10-tetracarboxylic dianhydride,reacting the resulting 1,7-dibromoperylene-3,4,9,10-tetracarboxylicdianhydride with cyclohexylamine, reacting theN,N'-dicyclohexyl-1,7-dibromoperylene-3,4,9,10-tetracarboxylic diimideformed in the course of imidation, with phenol, and subsequentlyhydrolyzing theN,N'-dicyclohexyl-1,7-diphenoxyperylene-3,4,9,10-tetracarboxylicdiimide.

                                      TABELLE                                     __________________________________________________________________________                                              Crude                                          t h or yield Purity  m.p.                                            Ex. R.sup.1 R.sup.2 R.sup.2' Amide III x g K V T° C. t.sub.1                                                                   h/t.sub.2 h in                                                                % in % Appearanc                                                              e [°         __________________________________________________________________________                                                              C.]                 1  --H  --H --H urea  20 Cu.sub.2 O                                                                        V1 180 4    70  80  dark red,                                                                              >300                                                                           microcrystallin                                                              e                     2  --CH.sub.3  --H  --H  N-methyl- 30 Cu.sub.2 O V1 180 4 98 80 dark                                                                  red, >300                                                                      ureamicrocrysta                                                              lline                 3  --CH.sub.3  --H  --H  N-methyl-      60  Cu.sub.2 O  V1  180      4                                                                    95     80                                                                     dark red,                                                                    >300                                                                                  urea                                                               microcrystalline      4  --CH.sub.3  --H  --H  N-methyl-      30  CuCl  V1  180      4                                                                      95     80                                                                     dark red,                                                                     >300                                            urea                                                                                                        microcrystalline      5  --CH.sub.3  --H  --H   N,N'-di-      15  Cu.sub.2 O  V1  180      4                                                                    95     90                                                                     dark red,                                                                    >300                                                                        methylurea                                                                    microcrystallin                                                              e                     6  --CH.sub.3  --H  --H   N,N'-di-      30  Cu.sub.2 O  V1  180      4                                                                    98     85                                                                     dark red,                                                                    >300                                                                       methylurea                                                                     microcrystallin                                                              e                     7  --CH.sub.3  --H  --H   N,N-di-       30  Cu.sub.2 O  V1  180      4                                                                    90     85                                                                     dark red,                                                                    >300                                                                       methylurea                                                                     microcrystallin                                                              e                     8  --CH.sub.3  --H  --H  N-methyl-      30  Cu.sub.2 O  V2  180    4/0                                                                    95     85                                                                     dark red,                                                                    >300                                                                                  urea                                                               microcrystalline      9  --C.sub.4 H.sub.9 --H  --H   N-butyl-      30  Cu.sub.2 O  V1  180                                                                    4      90                                                                   85       dark                                                                red,      >300                                                                 urea  microcrys                                                              talline                                                                        10 --C.sub.6                                                                 H.sub.11--H                                                                   --H   N-cyclo-                                                                    30                                                                        Cu.sub.2 O  V1                                                                180      6                                                                    80     85                                                                     orange-red,                                                                   >300                                         hexylurea                                                                                                      microcrystalline      11 --CH.sub.3  --H  --OPh N-methyl-      30  Cu.sub.2 O  V1  170      6                                                                    85     85                                                                     red-violet,                                                                  >300                                                                                 urea                                                               microcrystalline      12 --CH.sub.3  --OPh --OPh  N-methyl-   30  Cu.sub.2 O  V1  180     6                                                                     90     85                                                                     red-violet,                                                                  >300                                                                             urea                                                                     microcrystallin                                                              e                     13 --H   --H  --H   formamide   30  Cu.sub.2 O  V1  180     10       95                                                                   90                                                                        dark red,                                                                     >300                                                                          microcrystalline      14 --H   --H  --H   formamide  30  Cu.sub.2 O  V1  200     6       98                                                                   90       dark                                                               red,      >300                                                                   microcrystall                                                              ine                   15 --H   --H  --H   formamide  30  Cu.sub.2 O  V2  190    8/4      90                                                                   90       dark                                                               red,      >300                                                                      microcryst                                                              alline                16 --H   --H  --H   acetamide  30  Cu.sub.2 O  V1  180     14       70                                                                   80                                                                         dark red,                                                                     >300                                                                          microcrystalline      17  --Ph  --H  --H   acetani-    30  Cu.sub.2 O  V1  200      8      75                                                                   85                                                                        brown-red,                                                                    >300                     lide                                                       microcryst                                                              alline              __________________________________________________________________________

We claim:
 1. A process for preparing perylene-3,4-dicarboximides of theformula I: ##STR7## where R¹ is hydrogen; C₁ -C₈ -alkyl; C₅ -C₈-cycloalkyl; or phenyl or naphthyl, each of which can be substituted byC₁ -C₁₀ alkyl, C₁ -C₆ -alkoxy or cyano; andR² independently at eachoccurrence is hydrogen; C₁ -C₁₈ -alkyl; arylthio, 2-, 3- or4-pyridyloxy, 2-, 3- or 4-pyridylthio, 2-, 4- or 5-pyrimidyloxy or 2-,4- or 5-pyrimidylthio, each of which is optionally substituted by C₁-C₁₀ -alkyl, C₁ -C₆ -alkoxy or cyano, which comprises reacting aperylene-3,4,9,10-tetracarboxylic acid or its anhydride of the formulaII: ##STR8## with an amide of the formula III:

    R.sup.3 --CO--NHR.sup.1                                    III

in which R³ is hydrogen C₁ -C₄ -alkyl or --NR⁴ R⁵ where R⁴ and R⁵independently are hydrogen or one of the R¹ alkyls, cycloalkyls, phenylsor naphthyls and where if two or more of R¹, R⁴ and R⁵ are other thanhydrogen they are identical, in the presence of an inert diluent and atransition metal catalyst or a zinc metal or salt catalyst and undersuperatmospheric pressure.
 2. A process as claimed in claim 1, whereinthe diluent used is a tertiary nitrogen-basic compound.
 3. A process asclaimed in claim 1, wherein the diluent used is quinoline, isoquinolineor quinaldine.
 4. A process as claimed in claim 1, wherein thetransition metal catalyst used is metallic copper or an inorganic ororganic copper salt.
 5. A process as claimed in claim 1, which iscarried out under autogenous pressure.
 6. A process as claimed in claim1, which is carried out at from 120 to 250° C.
 7. The process as claimedin claim 1, wherein said metal catalyst is metallic copper, metalliczinc or an inorganic or organic salt of copper or zinc or a mixturethereof.